The scientists discovered that when parents “cleaned” a dropped pacifier by popping it into their own mouths, their children were less likely to develop allergies like asthma at 18 months than those who went without their parent’s saliva.

The study found that harmless bacteria transferred via pacifier from a parent’s mouth to their child's actually stimulated their immune system, helping the child build defenses to allergies.

The scientists looked at the pacifier-cleaning tactics of 184 infants and their parents, and swabbed the babies’ mouths starting at 4 months old.

Most parents reported that they rinsed the pacifier off in water after soiling it.

About half of parents reported boiling it in water occasionally, and nearly half said they had sucked the pacifier and given it back to the child at some point.

"There’s a certain ick factor there, but only if it’s not your habit," Ferdman said.

Allergies like eczema, asthma, food and inhalant allergies "were strongly reduced in children whose parents had this habit" of sucking a pacifier clean.

The hygiene hypothesis -- a practice of exposing children to harmless bacteria to build immunities -- has been around for almost 10 years, according to Ferdman, who also said studies showed children growing up on farms were less likely to develop allergies.

The researchers of the pacifier study began recruiting expecting parents in 1998, and took blood samples as well as interviewed the parents until the children were 36 months old.

Though the sample size of parents was small, the report noted that it was beneficial because the researchers were able to provide more detailed results.

Ferdman noted that the small sampling size might be a detractor, but a more important factor to look into would be the babies' other sucking habits -- like sharing eating utensils, kissing siblings, or sharing toys with other children at daycare facility that were likely slobbered on.

Dr. Ferdman doesn’t recommend that parents change their hygiene habits based on the study. As for his child-rearing habits: